419 research outputs found
Magnetohydrodynamic Simulations of the Atmosphere of HD 209458b
We present the first three-dimensional magnetohydrodynamic (MHD) simulations
of the atmosphere of HD 209458b which self-consistently include reduction of
winds due to the Lorentz force and Ohmic heating. We find overall wind
structures similar to that seen in previous models of hot Jupiter atmospheres,
with strong equatorial jets and meridional flows poleward near the day side and
equatorward near the night side. Inclusion of magnetic fields slows those winds
and leads to Ohmic dissipation. We find wind slowing ranging from 10%-40% for
reasonable field strengths. We find Ohmic dissipation rates ~10^17 W at 100
bar, orders of magnitude too small to explain the inflated radius of this
planet. Faster wind speeds, not achievable in these anelastic calculations, may
be able to increase this value somewhat, but likely will not be able to close
the gap necessary to explain the inflated radius. We demonstrate that the
discrepancy between the simulations presented here and previous models is due
to inadequate treatment of magnetic field geometry and evolution. Induced
poloidal fields become much larger than those imposed, highlighting the need
for a self-consistent MHD treatment of these hot atmospheres.Comment: 6 pages, 4 figures, accepted at ApJ
Three-dimensional atmospheric circulation of hot Jupiters on highly eccentric orbits
Of the over 800 exoplanets detected to date, over half are on non-circular
orbits, with eccentricities as high as 0.93. Such orbits lead to time-variable
stellar heating, which has implications for the planet's atmospheric dynamical
regime. However, little is known about this dynamical regime, and how it may
influence observations. Therefore, we present a systematic study of hot
Jupiters on highly eccentric orbits using the SPARC/MITgcm, a model which
couples a three-dimensional general circulation model with a plane-parallel,
two-stream, non-grey radiative transfer model. In our study, we vary the
eccentricity and orbit-average stellar flux over a wide range. We demonstrate
that the eccentric hot Jupiter regime is qualitatively similar to that of
planets on circular orbits; the planets possess a superrotating equatorial jet
and exhibit large day-night temperature variations. We show that these
day-night heating variations induce momentum fluxes equatorward to maintain the
superrotating jet throughout its orbit. As the eccentricity and/or stellar flux
is increased, the superrotating jet strengthens and narrows, due to a smaller
Rossby deformation radius. For a select number of model integrations, we
generate full-orbit lightcurves and find that the timing of transit and
secondary eclipse viewed from Earth with respect to periapse and apoapse can
greatly affect what we see in infrared (IR) lightcurves; the peak in IR flux
can lead or lag secondary eclipse depending on the geometry. For those planets
that have large day-night temperature variations and rapid rotation rates, we
find that the lightcurves exhibit "ringing" as the planet's hottest region
rotates in and out of view from Earth. These results can be used to explain
future observations of eccentric transiting exoplanets.Comment: 20 pages, 18 figures, 2 tables; Accepted to Ap
Meteorology of Jupiter's Equatorial Hot Spots and Plumes from Cassini
We present an updated analysis of Jupiter's equatorial meteorology from
Cassini observations. For two months preceding the spacecraft's closest
approach, the Imaging Science Subsystem (ISS) onboard regularly imaged the
atmosphere. We created time-lapse movies from this period in order to analyze
the dynamics of equatorial hot spots and their interactions with adjacent
latitudes. Hot spots are quasi-stable, rectangular dark areas on
visible-wavelength images, with defined eastern edges that sharply contrast
with surrounding clouds, but diffuse western edges serving as nebulous
boundaries with adjacent equatorial plumes. Hot spots exhibit significant
variations in size and shape over timescales of days and weeks. Some of these
changes correspond with passing vortex systems from adjacent latitudes
interacting with hot spots. Strong anticyclonic gyres present to the south and
southeast of the dark areas appear to circulate into hot spots. Impressive,
bright white plumes occupy spaces in between hot spots. Compact cirrus-like
'scooter' clouds flow rapidly through the plumes before disappearing within the
dark areas. These clouds travel at 150-200 m/s, much faster than the 100 m/s
hot spot and plume drift speed. This raises the possibility that the scooter
clouds may be more illustrative of the actual jet stream speed at these
latitudes. Most previously published zonal wind profiles represent the drift
speed of the hot spots at their latitude from pattern matching of the entire
longitudinal image strip. If a downward branch of an equatorially-trapped
Rossby waves controls the overall appearance of hot spots, however, the
westward phase velocity of the wave leads to underestimates of the true jet
stream speed.Comment: 33 pages, 11 figures; accepted for publication in Icarus; for
supplementary movies, please contact autho
Evolution of "51Peg b-like" Planets
About one-quarter of the extrasolar giant planets discovered so far have
orbital distances smaller than 0.1 AU. These ``51Peg b-like'' planets can now
be directly characterized, as shown by the planet transiting in front the star
HD209458. We review the processes that affect their evolution.
We apply our work to the case of HD209458b, whose radius has been recently
measured. We argue that its radius can be reproduced only when the deep
atmosphere is assumed to be unrealistically hot. When using more realistic
atmospheric temperatures, an energy source appears to be missing in order to
explain HD209458b's large size. The most likely source of energy available is
not in the planet's spin or orbit, but in the intense radiation received from
the parent star. We show that the radius of HD209458b can be reproduced if a
small fraction (~1%) of the stellar flux is transformed into kinetic energy in
the planetary atmosphere and subsequently converted to thermal energy by
dynamical processes at pressures of tens of bars.Comment: 11 pages including 9 figures. A&A, in press. Also available at
http://www.obs-nice.fr/guillot/pegasi-planets
The 8 Micron Phase Variation of the Hot Saturn HD 149026b
We monitor the star HD 149026 and its Saturn-mass planet at 8.0 micron over
slightly more than half an orbit using the Infrared Array Camera (IRAC) on the
Spitzer Space Telescope. We find an increase of 0.0227% +/- 0.0066% (3.4 sigma
significance) in the combined planet-star flux during this interval. The
minimum flux from the planet is 45% +/- 19% of the maximum planet flux,
corresponding to a difference in brightness temperature of 480 +/- 140 K
between the two hemispheres. We derive a new secondary eclipse depth of 0.0411%
+/- 0.0076% in this band, corresponding to a dayside brightness temperature of
1440 +/- 150 K. Our new secondary eclipse depth is half that of a previous
measurement (3.0 sigma difference) in this same bandpass by Harrington et al.
(2007). We re-fit the Harrington et al. (2007) data and obtain a comparably
good fit with a smaller eclipse depth that is consistent with our new value. In
contrast to earlier claims, our new eclipse depth suggests that this planet's
dayside emission spectrum is relatively cool, with an 8 micron brightness
temperature that is less than the maximum planet-wide equilibrium temperature.
We measure the interval between the transit and secondary eclipse and find that
that the secondary eclipse occurs 20.9 +7.2 / -6.5 minutes earlier (2.9 sigma)
than predicted for a circular orbit, a marginally significant result. This
corresponds to e*cos(omega) = -0.0079 +0.0027 / -0.0025 where e is the planet's
orbital eccentricity and omega is the argument of pericenter.Comment: 17 pages, 12 figure, accepted for publication in Ap
A Cytochemical Study of the Transcriptional and Translational Regulation of Nuclear Transition Protein 1 (TP1), a Major Chromosomal Protein of Mammalian Spermatids
Immunocytochemical localization and in situ hybridization techniques were used to investigate the presence of spermatid nuclear transition protein 1 (TP1) and its mRNA during the various stages of spermatogenesis in the rat. A specific antiserum to TP1 was raised in a rabbit and used to show that TP1 is immunologically crossreactive among many mammals including humans. During spermatogenesis the protein appears in spermatids as they progress from step 12 to step 13, a period in which nuclear condensation is underway. The protein is lost during step 15. An asymmetric RNA probe generated from a TP1 cDNA clone identified TP1 mRNA in late round spermatids beginning in step 7. The message could no longer be detected in spermatids of step 15 or beyond. Thus, TP1 mRNA first appears well after meiosis in haploid cells but is not translated effectively for the several days required for these cells to progress to the stage of chromatin condensation. Message and then protein disappear as the spermatids enter step 15. In agreement with a companion biochemical study (Heidaran, M.A., and W.S. Kistler. J. Biol. Chem. 1987. 262:13309-13315), these results establish that translational control is involved in synthesis of this major spermatid nuclear protein. In addition, they suggest that TP1 plays a role in the completion but not the initiation of chromatin condensation in elongated spermatids
Investigation of Jupiter's Equatorial Hotspots and Plumes Using Cassini ISS Observations
We present updated analysis of Jupiter's equatorial meteorology from Cassini observations. For two months preceding the spacecraft's closest approach, the ISS onboard regularly imaged the atmosphere. We created time-lapse movies from this period in order to analyze the dynamics of equatorial 5-micron hot spots and their interactions with adjacent latitudes. Hot spots are quasi-stable, rectangular dark areas on visible-wavelength images, with defined eastern edges that sharply contrast with surrounding clouds, but a diffuse western edge serving as a nebulous boundary with adjacent equatorial plumes. Hot spots exhibit significant variations in size and shape over timescales of days and weeks. Some of these changes correspond with passing vortex systems from adjacent latitudes interacting with hot spots. Strong anticyclonic gyres present to the south and southeast of the dark areas appear to circulate into hot spots. Impressive, bright white plumes occupy spaces in between hot spots. Compact cirrus-iike 'scooter' clouds flow rapidly through the plumes before disappearing within the dark areas. This raises the possibility that the plumes and fast-moving clouds are at higher altitudes, because their speed does not match previously published zonal wind profiles. Most profiles represent the drift speed of the hot spots at their latitude from pattern matching of the entire longitudinal image strip. If a downward branch of an equatorially-trapped Rossby waves controls the overall appearance of hot spots, however, the westward phase velocity of the wave leads to underestimates of the true jet stream speed. Instead, our expanded data set demonstrating the rapid flow of these scooter clouds may be more illustrative of the actual jet stream speed at these latitudes. This research was supported by a NASA JDAP grant and the NASA Postdoctoral Program
LEVONORGESTREL-RELEASING INTRAUTERINE SYSTEM IN ADENOMYOSIS; PREDICTORS FOR RESPONSE AND CLINICAL OUTCOME
Objectives: The aim is to detect clinical and ultrasonographic characters that predict the response of adenomyosis to levonorgestrel-releasing intrauterine system (LNG-IUS) and to evaluate the clinical efficacy and the time needed to show a response.Methods: A prospective single-arm study conducted in the Obstetrics and Gynaecology Department Al-Yarmouk Teaching Hospital in Baghdad/Iraq from August 2015 to March 2018. Women with symptomatic adenomyosis with age 39 years and above and who completed their families had been enrolled in this study. LNG-IUS was used as a treatment; the outcome measure was to evaluate its effect in improving the symptoms and the time needed to show a clinical response. Multivariate analysis was used to assess the contribution of the clinical and ultrasonographic parameters to the prediction of the response to LNG-IUS.Results: Over the mean duration of follow-up period of the study (22.7±9.9 months), there was a significant improvement in menstrual blood loss, dysmenorrhea, and hemoglobin (Hb) with significant decrease in uterine volume (p˂0.001). The time to show response was as early as 3 months and the first 6 months is the best time to predict failure. Initial menstrual blood loss and Hb were good predictors to show response while uterine volume an excellent one (positive predictive value 80% and negative predictive value 97.2%).Conclusion: Levonorgestrel-releasing intrauterine device is an effective treatment of symptomatic adenomyosis in term of time to response and duration of response. The presenting Hb, menstrual blood loss, and uterine volume are useful predictors of response
- …